Explanation
There are 3 values in the SNMPv3 header that must match for the communication to take place:
snmpEngineID, snmpEngineTime, snmpEngineBoots. The error received indicates a problem with the EngineID value: "authentication failure, Unknown Engine ID" To specify the Engine ID, we can use the command "show snmp user". The following example specifies the username as abcd with Engine ID: 00000009020000000C025808:

The "debug snmp packet" command displays all SNMP packets that are arriving and being replied to.